1. Field of the Invention
The present general inventive concept relates to a method and apparatus to transmit signals in a communication system.
2. Description of the Related Art
In conventional communication systems, the following two methods may be used to improve intelligibility of speech signals. A first method involves canceling noise signals at a transmitter, and a second method involves increasing a sound pressure level (SPL) of speech signals at a receiver.
Of the two methods, the first method of canceling noise signals at a transmitter will be described below.
A transmitter signal, which is a speech source signal, is input to a conventional transmitter. The transmitter signal includes a speech signal (hereinafter referred to as a “transmitter speech signal”) and/or a noise signal (hereinafter referred to as a “transmitter noise signal”). Therefore, the transmitter cancels the transmitter noise signal from the transmitter signal to prevent the intelligibility level of the transmitter speech signal from dropping due to the transmitter noise signal.
The transmitter transmits the transmitter speech signal, from which the transmitter noise signal is cancelled, to a receiver. Then the receiver can receive a more articulated speech signal, by receiving the transmitter signal from which the transmitter noise signal is cancelled, from the transmitter.
The second method of increasing a sound pressure level of a speech signal at the receiver to improve intelligibility of the speech signal will be described.
Sound pressure level, or SPL, is a measure of a deviation of pressure from a reference level. The reference level may be an ambient level, or a level at which a human may hear the speech, for example. A speech pressure level may be measured by a microphone when the speech is travelling through air.
A receiver signal, which is a speech source signal, is input into a conventional receiver. The receiver signal, like the transmitter signal, includes a speech signal (hereinafter referred to as a “receiver speech signal”) and/or a noise signal (hereinafter referred to as a “receiver noise signal”). The receiver predicts or analyzes the receiver noise signal from the receiver signal.
When the transmitter signal is received, the receiver increases a sound pressure level of the received transmitter speech signal to prevent an intelligibility level of the transmitter speech signal from falling due to the receiver noise signal. The intelligibility level measured by a ratio of speech to noise in a signal. For example, if a signal has a speech signal with a high magnitude relative to a noise signal, it has good intelligibility or a high level of intelligibility.
Therefore, since the output receiver speech signal is greater in intensity than the receiver noise signal at the receiver, a user of the receiver can listen to a more articulated receiver speech signal.
In this way, in the conventional communication system, the process of canceling the transmitter noise signal at the transmitter and the process of increasing an SPL of the received transmitter speech signal at the receiver are performed independently to improve intelligibility of the speech signal.
However, cancelling the noise signal may cause a variation in the transmitter, and when the sound pressure level of the received transmitter speech signal is increased at the receiver, a variation in the transmitter speech signal may once again. In other words, cancelling the noise signal at the receiver may cause a first variation of a speech signal, and increasing a sound pressure level may cause another variation of the same speech signal.
As a result, in the conventional communication system, as the transmitter and the receiver individually use the methods to improve intelligibility of the speech signal, the speech signal may be subject to variation twice.
Meanwhile, in the conventional communication system, when canceling the noise signal from the transmitter signal, the transmitter should accurately determine a noise signal cancellation, i.e., an amount of the noise signal it will cancel based on a predicted noise signal.
If the determined noise signal cancellation is greater than an actual noise signal level, the speech signal may be distorted. However, when the determined noise signal cancellation is less than the actual noise signal level, the noise signal may still exist.
When the noise signal cancellation cannot be exactly determined, intelligibility of the speech signal may deteriorate. Hence, there is a need for a method and apparatus to accurately determine the noise signal cancellation in the conventional communication system.